On Wed, Jun 21, 2000 at 09:04:49AM -0700, Jeff Bailey wrote:
> On Tue, Jun 20, 2000 at 05:25:08PM -0400, Olivier Galibert wrote:
>
> > > Now, can't this be done by setting up a direct communication channel
> > > between two userspace processes? With a semaphore you can check on
> > > incoming messages, etc. This way you only need to do a context-switch if
> > > you ask the kernel to set up a direct message-channel.
> >
> > Bzzt wrong. Going userspace->kernel and back does not involve any
> > context switch. It's going userspace->another userspace that does.
>
> Really? I thought I remembered Tanenbaum's book "Modern Operating
> Systems" saying that this was one of the problems with drivers in
> Userspace. It's been a while since I've read it, so I might be wrong. =)
Yep, drivers being in said "another userspace". That does not
contradict what I said.
OG.
